Nitrogen oxides （NOx） emission during the regeneration ofcoked fluid catalytic cracking （FCC） catalysts is an en- vironmental issue. In order to identify the correlations between nitrogen species in coke and diffe...Nitrogen oxides （NOx） emission during the regeneration ofcoked fluid catalytic cracking （FCC） catalysts is an en- vironmental issue. In order to identify the correlations between nitrogen species in coke and different nitrogen- containing products in tail gas, three coked catalysts with multilayer structural coke molecules were prepared in a fixed bed with model compounds （o-xylene and quinoline） at first. A series of characterization methods were used to analyze coke, including elemental analysis, FT-IR, XPS, and TG-MS. XPS characterization indicates all coked catalysts present two types of nitrogen species and the type with a higher binding energy is related with the inner part nitrogen atoms interacting with acid sites. Due to the stronger adsorption ability on acid sites for basic nitrogen compounds, the multilayer structural coke has unbalanced distribution of carbon and ni- trogen atoms between the inner part and the outer edge, which strongly affects gas product formation. At the early stage of regeneration, oxidation starts from the outer edge and the product NO can be reduced to N2 in high CO concentration. At the later stage, the inner part rich in nitrogen begins to be exposed to 02. At this period, the formation of CO decreases due to lack of carbon atoms, which is not beneficial to the reduction of NO. There- fore, nitrogen species in the inner part of multilayer structural coke contributes more to NOx formation. Based on the multilayer structure model of coke molecule and its oxidation behavior, a possible strategy to control NOx emission was discussed merely from concept.展开更多
Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct...Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado （CO） in the U.S. Central Great Plains, and an Alfisol from Virginia （VA） in the southeastern USA following the application of switchgrass （Panicum virgatum） biochar. The switchgrass biochar was applied at four levels, 0%,0, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha^-1, respectively, to the soils grown with wheat （Triticum aestivum） in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen （N） content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester （FAME） profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from -2.1 to -38.4 mg kg^-1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus （P）, and extractable potassium （K） in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 457o and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi：bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon （C）.展开更多
基金Supported by the National Natural Science Foundation of China(21476263)the National Natural Science Foundation for Young Scholars(21206198)
文摘Nitrogen oxides （NOx） emission during the regeneration ofcoked fluid catalytic cracking （FCC） catalysts is an en- vironmental issue. In order to identify the correlations between nitrogen species in coke and different nitrogen- containing products in tail gas, three coked catalysts with multilayer structural coke molecules were prepared in a fixed bed with model compounds （o-xylene and quinoline） at first. A series of characterization methods were used to analyze coke, including elemental analysis, FT-IR, XPS, and TG-MS. XPS characterization indicates all coked catalysts present two types of nitrogen species and the type with a higher binding energy is related with the inner part nitrogen atoms interacting with acid sites. Due to the stronger adsorption ability on acid sites for basic nitrogen compounds, the multilayer structural coke has unbalanced distribution of carbon and ni- trogen atoms between the inner part and the outer edge, which strongly affects gas product formation. At the early stage of regeneration, oxidation starts from the outer edge and the product NO can be reduced to N2 in high CO concentration. At the later stage, the inner part rich in nitrogen begins to be exposed to 02. At this period, the formation of CO decreases due to lack of carbon atoms, which is not beneficial to the reduction of NO. There- fore, nitrogen species in the inner part of multilayer structural coke contributes more to NOx formation. Based on the multilayer structure model of coke molecule and its oxidation behavior, a possible strategy to control NOx emission was discussed merely from concept.
文摘Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado （CO） in the U.S. Central Great Plains, and an Alfisol from Virginia （VA） in the southeastern USA following the application of switchgrass （Panicum virgatum） biochar. The switchgrass biochar was applied at four levels, 0%,0, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha^-1, respectively, to the soils grown with wheat （Triticum aestivum） in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen （N） content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester （FAME） profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from -2.1 to -38.4 mg kg^-1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus （P）, and extractable potassium （K） in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 457o and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi：bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon （C）.
